Water coolers are well known for providing fresh, cold bottled water in office, domestic or other environments. Some prior art bottled water delivery systems are also capable of heating and even boiling water for the purpose of making coffee, tea, etc. Prior art water coolers typically comprise a housing which contains a water reservoir at the top, a water delivery faucet connected to the reservoir and having a trigger-operated spigot or spout for user-controlled pouring of water from the reservoir into a cup, pot, etc. A water tank or bottle is mounted on top of the housing in an inverted position so that the neck portion of the tank or bottle extends downwardly into the reservoir. In operation, water flows through the neck into the reservoir while air flows into the tank or bottle through the neck in order to equalize pressure inside and outside of the tank. When the water level in the reservoir rises to cover the mouth of the neck, air can no longer enter the tank through the neck and water ceases flowing from the tank into the reservoir. In response to user activation of the faucet, the water level in the reservoir drops thereby opening the mouth of the tank which permits water to flow out of the tank and air to flow into the tank for replenishing the water level in the reservoir until the water level again rises to the mouth of the neck.
One disadvantage of such prior art water coolers is that it is not possible to attach a water filter to the neck of the tank or bottle for filtering the water as it is dispensed, since air is not capable of passing through conventional filter material.
In an effort to overcome this disadvantage of the prior art water coolers, one system is known in which a water filter attachment is provided to the neck of a water bottle or tank in combination with a one-way air valve for admitting air into the tank. According to this system, the one-way air valve is in the form of a hollow tube which tapers at the top to a diameter which is small enough that surface tension prevents water from flowing therethrough, but is large enough to permit air to flow into the tank.
The above-identified prior art system suffers from a number of disadvantages. The one-way valve is time consuming to install and therefore labour intensive, and is of awkward shape which makes packaging difficult. The valve is of delicate design which lacks robustness and is potentially unreliable.